1. Field of the Invention
This invention relates to nerve tissue stimulation and infusion techniques, and more particularly relates to such techniques for treating addictions.
2. Description of Related Art
In 1954 Olds and Milner demonstrated the reward circuits of the brain by electrical stimulation of the septal area of the brain ("Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain.", J Comp Physiol Psychol 47:419-427, 1954) This study marked the beginning of research to understand the nature of addiction.
There are several addicting substances. Addictive substances including opiates, such as heroin, opium and morphine, the sympathomimetics, including cocaine and amphetamines, the sedative-hypnotics including alcohol, benzodiazepines and barbiturates and nicotine which has effects similar to opiods and sympathomimetics. Drug dependence is contrasted with drug abuse by the hallmark symptoms of addiction. Drug addiction is characterized by two features, a craving or compulsion to take the drug and an inability to limit intake of the drug. Additionally, drug dependence is associated with tolerance, which is the loss of effect of the drug with repeated administration and withdrawal, defined as the appearance of physical and behavioral symptoms when the drug is not consumed following chronic use. Sensitization occurs if the repeated administration of a drug leads to an increased response to each dose. Tolerance, sensitization, and withdrawal are phenomena reflecting some sort of plastic change occurring in the central nervous system in response to continued use of a substance. This change is presumably an unstable process that somehow captures the normal mechanisms mediating reinforcement and reward of behavior to motivate the addicted individual to continue consuming the drug in the face of serious social, legal, physical and professional consequences.
Researchers in the field of drug dependence and reward have identified neurological substrates involved in animal motivation and reward and how the neural mechanisms of these substrates are co-opted to result in an addictive state (George F. Koob, "Drugs of abuse: anatomy, pharmacology and function of reward pathways. TiPS--May 1992[Vol. 13]) The mesolimbic dopamine system which innervates the nucleus accumbens has been determined to be the portion of the brain which plays a critical role in mediation of the reinforcing aspects of addiction and the reinforcing aspects of withdrawal.
One theory of how the addictive process occurs is the opponent-process theory. The opponent-process theory describes a process of decreasing positive reward because of increasing tolerance to the consumption of the addicting substance coupled with an increasing negative reinforcement due to withdrawal. The negative reinforcement associated with withdrawal is a motivating factor for continuing consumption of the addicting substance. These processes represent adaptive changes in the nervous system. Memory of the positive reinforcement or "high" coupled with environmental cues which have become conditional positive reinforcers can lead to a relapse of addictive behavior. Researchers have recently recognized certain destructive behaviors such as gambling, shopping, eating and sexual preoccupation collectively referred to as "impulse control" disorders which manifest a common set of symptoms with chemical addictions.
Electrical stimulation of nervous tissue has been used to treat the negative reinforcing symptoms associated with withdrawal from an addictive substance. Transcutaneous nerve stimulation has been proposed as a means of relieving the symptoms of withdrawal form an addictive substance. U.S. Pat. Nos. 3,946,745, 4,841,973, 4,865,048, 5,458,625, and 5,593,432 describe methods and apparatus for stimulating the skin surface e.g. behind the ear to relieve symptoms of addiction. These techniques are described as a more advanced form of acupuncture and are reported to relieve withdrawal symptoms in particular.
Transcranial electrical fields have been applied to the brain (U.S. Pat. No. 4,646,744) to depolarize nerve cells as a means of treating addictions. The effects of transcranial electrical stimulating fields on withdrawal from addictive substances has been enhanced by the coadministration of neuroactive chemical promoter (U.S. Pat. No. 5,084,007).
Certain pharmaceutical agents have been administered to affect the addictive process. Mayer et. al (U.S. Pat. No. 5,556,838) teaches the use of nontoxic NMDA blocking agents coadministered with an addicting substance to prevent the development of tolerance or withdrawal symptoms. The agents are administered acutely through an oral, intravenous, intrathecal, epidural, or intraventricular route. Rose and Levin (U.S. Pat. No. 5,574,052) teaches coadministration of the addictive substance with an antagonist to partially block the pharmacological effects of the substance. The preferred mode of delivery is a transcutaneous patch. Mendelson and Mello propose use of a mixed opiate agonist/antagonist to treat cocaine and opiate addiction. Downs (U.S. Pat. No. 5,232,934) teaches administration of 3-phenoxypyridine to treat addiction. Imperato and Romer (U.S. Pat. Nos. 5,039,680 and 5,198,459) teach the use of a serotonin antagonist as a treatment for chemical addiction. Nestler et. al. teach the infusion of the growth factors BDNF or NT-4 to inhibit or reverse the neurological adaptive changes that correlate with the behavioral changes of an addictive disorder.
Inotophoretic delivery through the skin of agents to treat addiction is described in U.S. Pat. Nos. 5,415,629 and 5,538,503. Alternatively, Yolles teaches delivery of drugs to treat addictions by eluting them from a polymeric material preferably implanted under the skin. (Curt he does describe lining a catheter or injecting into blood stream--can I focus on the subcutaneous application???)
Alternatively, Sagen (U.S. Pat. No. 5,762,925) teaches implantation of encapsulated adrenal medullary cells into the central nervous system so that they might release substances that inhibit the development of opiod intolerance.